In today's PMR technology, an all wrapped around (AWA) shield writer is widely used by the major hard disk drive (HDD) manufacturers. The function of a trailing shield in an AWA structure is to improve the magnetic field gradient along a down track direction that is a key requirement for high bits per inch (BPI). Meanwhile, side shields and a leading shield serve to define a narrower writer bubble that is important for realizing higher tracks per inch (TPI). In hard disk drives, ATE is one of the most critical issues to be addressed for optimizing the performance of PMR writers. Both micromagnetic modeling described by S. Song et al. in “Micromagnetic analysis of adjacent track erasure of wrapped-around shielded PMR writers”, IEEE Trans. Magn., vol. 45, No. 10, pp. 3730-3732 (2009), and experimental data provided by Y. Tang et al. in “Characterization of adjacent track erasure in perpendicular recording by a stationary footprint technique”, IEEE Trans. Magn., vol. 49, No. 2, pp. 744-750 (2013) indicate that one of the root causes for ATE is the stray field from side shields during the dynamic writing cycles. ATE was found to have a strong dependence on writing frequency. As a result, more severe ATE issues are expected as HDD technology moves toward ultra-high data rates in the near future.
Magnetic side shields in conventional PMR writers have an elongated shape along the cross-track direction at the ABS, and this design induces shape anisotropy in the cross-track direction. Accordingly, the magnetization of magnetic material in the side shields will also be along the cross-track direction due to shape anisotropy. During a HDD dynamic magnetic recording process, magnetic flux generated from the main pole tip of the PMR writer will drive the two side shields along the cross-track direction at a very high frequency (˜1 GHz). Both of the modeling and experimental studies from the aforementioned references show that strong stray field leakage from side shields is closely coupled with the domain formation, especially the initial magnetization direction in the side shields at high frequency magnetic switching. Based on experimental results, 180 degree magnetization rotations occur when the driving magnetic flux is opposite to the initial magnetization along the cross-track direction. These rotations produce magnetic charge that in turn causes stray field leakage from the side shields. Therefore, an improved magnetic shield structure is required that controls domain formation (initial magnetization direction) in side shields and thereby avoids the 180 degree magnetization rotations to enable improved ATE.